The invention proceeds from a method for operating a diesel internal combustion engine according to the preamble of patent claim 1.
In the preamble of patent claim 1 the invention refers to a prior art, such as is known from the publication: Proc Instn Mech Engrs 1973, Vol. 187 35/73, pp 425-434. There, additional air from a compressed-air reservoir is supplied to the compressor of a turbocharger of a diesel internal combustion engine. This additional air serves for eliminating the lack of combustion air under part load, particularly in the case of a reduced engine rotational speed and in the transient mode. One disadvantage of this is that this additional air excites blade vibrations in the compressor wheel of the compressor. When the compressor wheel is accelerated, an undesirable time delay occurs.
Several types of starting for bringing a diesel engine to the starting rotational speed necessary for the spontaneous ignition of the fuel are indicated in the Technischen Handbuch Dieselmotoren [Technical Manual for Diesel Engines], published by Prof. Dr.-Ing. Rudolf Sperber, 4th edition, VEB Verlag Technik Berlin 1986, pp 99-108. Larger engines employ starting by means of compressed air from a starting-air bottle with a pressure of 3 MPa via a pressure reducing valve, a central air distributor and starting valves arranged in the cylinder heads. The starting valves are spring-loaded nonreturn valves which close immediately when ignitions commence and which, in the case of reversible engines, are controlled via a camshaft. At the beginning of starting, the diesel engine operates as a compressed-air engine. The starting-air bottles may be filled up via a charging valve of an engine cylinder or by means of a compressor installed independently of the engine. A supply of additional air after the engine has been started is not disclosed.
CH 624182 A5 discloses a multicylinder diesel internal combustion engine, in which, during starting and also in the part-load mode, a higher compression and therefore better ignition conditions are achieved in some cylinder units by the remaining cylinder units temporarily being used as compressors. One disadvantage of this is that, during this mode, only some of the cylinders of the engine are available for delivering the desired power.
It is known from EP 0367406 A2 to achieve a pressure rise in the cylinder of the diesel internal combustion engine by means of a turbocharger which is driven by exhaust gases of the latter. Arranged on the shaft of the turbocharger is the rotor of an electric machine which is operated as an externally fed motor during starting or when the diesel internal combustion engine falls below a predeterminable minimum rotational speed and is otherwise operated as a generator. This solution is highly complicated.
As regards the relevant prior art, reference is made to the publication of Hans-Josef Schiffgens et al., xe2x80x9cDie Entwicklung des neuen MAN BandW Diesel-Gas-Motors 32/40 DGxe2x80x9d [xe2x80x9cThe Development of the new MAN BandW diesel gas engine 32/40 DGxe2x80x9d] in: MTZ Motortechnische Zeitschrift 58 (1997) 10, pp 584-590, from which a diesel gas engine is known, in which a fuel gas is supplied under relatively low pressure to the air inlet duct of the diesel internal combustion engine. The gas valve is controlled electronically, opened hydraulically and closed by spring force.
The so-called Miller method is known inter alia from the book by K. Zinner, xe2x80x9cAufladung von Verbrennungsmotorenxe2x80x9d [xe2x80x9cSupercharging of internal combustion enginesxe2x80x9d], 2nd edition, Springer-Verlag Berlin Heidelberg New York 1980, pp 221-228. In this method, the air inlet valve (VE) closes before the bottom dead center (UT) of the piston of the diesel internal combustion engine, as indicated in FIG. 2 by a closing line (21xe2x80x2) illustrated by dashes. When an engine is operating with fixed control times by the Miller method, serious air deficiency phenomena may arise in the lower load range.
The invention, as defined in patent claim 1, achieves the object of specifying a more cost-effective method for operating a diesel internal combustion engine of the type initially mentioned, which makes sufficient combustion air available in all the cylinders even under part load and in transient operating states.
Advantageous refinements of the invention are defined in the dependent patent claims.
One advantage of the invention is that the diesel internal combustion engine operates more effectively in all operating states, in particular that emissions and thermal loads are reduced.
According to an advantageous refinement of the invention, devices present for starting may also be used for subsequent operation and a plurality of gas inlets for starting gas and additional gas may be provided for each cylinder of the diesel internal combustion engine.